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TPS23753A: some problem related to efficiency

Zhanpeng Li
Intellectual 2140 points
Part Number: TPS23753A

Hi Team,

customer were facing a problem related to low efficiency. 

end equipment: Digital microphone with using POE as power supply. since the customer end product is in small package so the power loss and themral preformance is important.

when test the efficiency, they found that the efficiency is only about 62% with 5V@300mA output. attached the testing data as follow

from left to righ, you can find input voltage, input current(mA),input power, output voltage, output current and efficiency.

we tried to reduce the switching frequency from250khz to 50khz, it do can improve the efficiency and it bring a large disturb(600hz to 2khz) when microphone is recording.

here we have some support need:
1) can you give us some comment related to the schemtic i attached below? which may improve the performance?

2)with 250khz switching frequency, whether this is abnormal when R388 is serious heating? how can we change or improve the thremal proformance?

3)after changing switching frequency to 50khz, How can we adjust the circuit to reduce the disturb 

PD线路.pdf

BR

Brandon.

  • 0
    TI__Mastermind 21320 points

    Hello Zhanpeng,

    62% at 5V/300mA is low, but there are ways we can improve it.

    1. The customer choose to do a diode rectified flyback. These are inherently less efficient but more cost effective. I would recommend switching to a synchronous flyback (that uses a FET instead of a diode). 

    The good news is the TPS23753A has multiple "efficiency optimized" designs to choose from. They are all synchronous flybacks. 

    https://www.ti.com/tool/PMP8896

    https://www.ti.com/tool/PMP9175

    https://www.ti.com/tool/TIDA-00079

    2. R388 is currently acting as a snubber across the primary FET. It is expected it will get hot. These components should be large size, at least 1206 if not bigger since large currents/voltage is dissapated across it. Typically, most designs populate the DRC snubber (R320, C261 & D17). The RC snubber is much less common, and I've only seen it used in conjunction with the DRC, not in place of. 

    3. I would highly encourage keeping the design switching at 250kHz. Again, the customer is at a disadvantage with the current topology. Diode rectified flybacks are typically cost effective choices, and synchronous flybacks are more efficient. Even if the customer stays with the diode rectified solution, I would not recommend the lower switching frequency because of these oscillations. These appear at lower switching frequencies so it is not recommended. 

    If this post answers your question, please indicate so by marking this thread as resolved. Thank you.

     

    Regards, 

     

    Michael P.

    Applications Engineer

    Texas Instruments